Polyesteramides are polymers containing both ester linkages and amide linkages. Their significance to the technology of medical devices stems from the fact that the susceptibility of their ester linkages to hydrolysis confers upon them the ability to be eventually absorbed or resorbed by a body into which they have been implanted and their amide linkages confer upon them the desirable mechanical properties characteristic of polyamides.
Certain fiber-forming polyesteramides obtained from the single stage reaction of approximately equimolar amounts of a monoalkanolamine and a dicarboxylic acid are described, for example, in U.S. Pat. No. 2,386,454.
Other polyesteramides, disclosed in U.S. Pat. No. 4,226,243, have been indicated to be useful for the manufacture of absorbable suture and other surgical devices. These polyesteramides are obtained from the reaction of a dicarboxylic acid ester with a bis-oxyamidodiol, the latter of which is derived from the reaction of diethyl oxalate with a monoalkanolamine, such as ethanolamine.
U.S. Pat. No. 4,343,931 discloses absorbable surgical devices manufactured from polyesteramides which are obtained in a multi-step process by first reacting a diamine with lactic or glycolic acid to produce a diamidediol, and subsequently reacting the diamidediol with a bischloroformate or a compound selected from the group consisting of dicarboxylic acids, diacidchlorides, and dicarboxylic acid dianhydrides to provide the polyesteramide compounds.
U.S. Pat. No. 3,025,323 describes water-soluble amide diols derived from lactone monomers and monoalkanol amines that may be used as intermediates in the preparation of polymers. These intermediates are also disclosed as being useful as sizing additives for paper, leather, or other porous materials.
U.S. Pat. No. 6,120,788 describes fiber-forming bioabsorbable polyesteramides made by the polymerization of diamide diols with 3,6-dioxaoctanedioic acid. Certain of these polymers are said to be useful for the production of surgical sutures having performance characteristics that may include low bending stiffness. They are also disclosed as being useful in the production of other fiber-based bioabsorbable implants and molded devices.
U.S. Pat. No. 5,902,874 describes cyclic monomer derived polyesteramides, which are disclosed as being useful for manufacture into shaped articles for use, for example, as surgical devices.
U.S. Pat. No. 5,914,387 describes shaped articles which are prepared from polyesteramides and which are disclosed as being useful as surgical devices. The disclosed polyesteramides have amino acid-derived groups alternating with hydroxy acid-derived groups.
U.S. Pat. No. 5,919,893 describes polyesteramides which are disclosed as being suitable for use in biomedical applications and which may be obtained by reacting a diamino alkyl ester with an alpha-hydroxy acid to form a diamide diol which may be further reacted with an acyl halide or dicarboxylic acid to provide the polyesteramide.
Shaped articles made from nylon have been widely accepted for a variety of applications, including some biomedical applications. Generally speaking, nylon refers to a family of high strength, resilient synthetic polymeric materials containing recurring amide groups in the polymer backbone. While nylon polymers have certain useful properties, shaped articles based on nylon are not typically bioabsorbable and may therefore be unacceptable in circumstances that require bioabsorption. For example, certain biomedical applications, such as surgical devices including but not limited to monofilament and multifilament sutures, films, sheets, plates, clips, staples, pins, screws, stents, stent coatings, and the like, require a material that is bioabsorbable.
In addition, high strength, highly flexible, tough, and durable fibers that possess a prolonged flex fatigue life are needed for use as braided, knitted, woven, or non-woven implants to augment and/or temporarily reinforce autologous tissue grafts or to serve as scaffolds for tissue regeneration. One example of such an implant is known as a ligament augmentation device (LAD) used to reconstruct the anterior cruciate ligament (ACL) of the knee. Bioabsorbable fibers of the prior art, such as poly(L-lactic acid) (PLA), have not been successful in this application due to low flex fatigue life, shedding of wear debris due to the brittle nature of the fibers, and prolonged bioabsorption time.
Other well known uses for bioabsorbable polymers that have not been fully realized or perfected with available polymers of the prior art include scaffolds for tissue engineering, bioabsorbable knitted vascular grafts, drug-releasing devices, growth factor-releasing implants for bone and tissue regeneration, and fiber-reinforced composites for orthopedic applications. For example, composites of polymers reinforced with dissimilar materials, such as dissolvable glass fiber reinforced poly(lactic acid) are generally unacceptable for use as implants. Although dissolvable glass fibers provide high modulus needed for the composite to have high initial strength and stiffness, adhesion between glass and polymer may invariably fail prematurely in vivo resulting in devices with unacceptable in vivo performance.
Self-reinforced composites were developed as an alternative to composites of polymers reinforced with dissimilar materials, such as those described above. In self-reinforced fiber composites, both reinforcing fibers and matrix are generally made of the same material. Although the stiffness is lower than can be achieved with glass fibers, this alternative type of composite ensures good adhesion between fiber and matrix and thus may offer the possibility of longer lasting in vivo strength. Self-reinforced poly(glycolic acid) (PGA) rods, pins and screws made by hot pressing or sintering PGA fibers have shown promise in clinical use. The main disadvantage of PGA in general is that it typically degrades at too fast a rate for orthopedic applications and releases an excessive concentration of acidic degradation products into the surrounding tissue.
Despite advancements in the art of producing polymeric materials and methods for making polymeric materials suitable for use in sutures, molded devices, and similar surgical articles, presently available polymers generally lack adequate performance properties desirable in surgical articles, for example, those related to bioabsorption, flex fatigue life, strength in use, flexibility and/or durability. Thus, there continues to be a need for new fibers that are monofilament, have high initial tensile knot strength, retain useful strength in vivo for a period of time, for example, about two weeks or longer, are fully bioabsorbed within a few months after strength loss, and have very low bending stiffness. There is also a need for surgical article materials that have strength and resiliency characteristics comparable to that of nylon, but which are also bioabsorbable. It would be particularly advantageous to provide surgical article materials having tunable physical and/or biological properties, so that surgical articles having a variety of end uses can be prepared. The present invention is related to these and other important ends.